There is a known video analysis system which includes a monitoring camera to be installed and monitors a moving object such as a person moving in a monitored area for the purpose of crime prevention, disaster prevention, and so on. For example, it is proposed as a first related technique relating to the present invention to compare a frame image of a video image shot by a monitoring camera with a last frame image, extract a difference between the frame images, and detect a moving object such as an intruder based on the extracted difference (see Patent Document 1, for example).
On the other hand, the following techniques are proposed as other techniques relating to the present invention.
First, it is proposed as a second related technique relating to the present invention to acquire camera information and related information which are acquired or inputted in shooting an image, estimate the scene of the image by using the camera information and the related information, and execute predetermined image processing appropriate to the estimated image scene (see Patent Document 2, for example). According to this second related technique, it is possible to correct data of a shot image in accordance with a shooting environment and increase the quality of the image.
Further, the following image correction system is proposed as a third related technique relating to the present invention. The image correction system includes an information acquisition part which acquires state information showing a state in which a photograph has been shot, a correction parameter selection part which selects a plurality of correction parameters based on the state information, and an image quality correction part which executes an image data correction process by using the selected correction parameters. According to the third related technique, it is possible to alter the quality of a shot image in accordance with a shooting environment.
Patent Document 1: Japanese Unexamined Patent Application Publication No. JP-A 2011-077617
Patent Document 2: Japanese Unexamined Patent Application Publication No. JP-A 2011-238177
Patent Document 3: Japanese Unexamined Patent Application Publication No. JP-A 2010-171661
When a video analysis system as mentioned above is used, a monitoring camera which acquires video data may be installed outdoors, for example, on the street or around the entrance. When the monitoring camera is thus installed outdoors, the environment of a place where the monitoring camera is installed change under the influence of change of the outdoor environment. In other words, when the monitoring camera is installed outdoors, the environment of the installation place greatly varies depending on, for example, whether it is fine or rainy, whether it is in the daytime or at night, and whether the wind is blowing or not. When the environment of the place where the monitoring camera is installed changes, video data acquired by the monitoring camera changes. For example, the shadow of a moving object is clearly shown on a fine day, but the shadow is not shown on a cloudy day. On a windy day, trees or the like on the background largely swings.
Therefore, it is desired to prevent the accuracy of detection of a moving object from being affected even when the environment of a place where a monitoring camera is installed changes and video data changes.
In order to deal with such a problem, it is possible to consider applying the second or third related technique to the first related technique and correcting data of a shot image in accordance with the shooting environment to increase or change the quality of the image. However, increase or alteration of the quality of an image does not necessarily lead to increase of the analysis performance of a video analysis system. For example, when the quality of image data including a person as a subject is increased by using the abovementioned techniques, a portion corresponding to the shadow of the person is also shown sharply. As a result, a video analysis system may falsely detect the sharply shown portion corresponding to the shadow of the person as a moving object. Thus, for a video analysis system, simple increase or alteration of the quality of an image does not always lead to increase of the analysis performance.
Thus, a video analysis system has a problem that change of the environment of installation of a monitoring camera and change of video data may affect the accuracy of detection of a moving object.